Process for the removal of metal powder and low metal oxides from the surfaces of bundles of wire which have been etched with sodium hydride

ABSTRACT

Improvement in the known process for removing rust or scale from metal objects, especially wires, by immersion of the object in caustic soda, caustic potash, or a mixture thereof, followed by inducing an electric current to pass therethrough while maintaining the object in an alkaline medium which improvement involves using lye of at least 60 percent concentration as the alkaline bath and operating at up to about 25* C. over the solidification point of the alkaline bath.

O United States Patent [1113,616,342

[72] Inventors Arnold Lenz [56] References Cited Q Z Q M H h f UNITEDSTATES PATENTS 1,600,355 9/1926 Otis et a1 204/145 A 1 No 690 2,377,8766/1945 Gilbert 204/145 X 2,468,006 4/1949 Webster 204/145 [22] Med 19672 847 374 8/1958 Webster eta] 204/145 [45] Patented Oct. 26, 1971 [73]Assignee Dynamit Nobel Aktiengesellschaft FOREIGN PATENTS Troisdorf,Germany 502,176 4/1951 Belgium 204/145 [32] Priority Dec. 10, 1966155,712 10/1961 U.S.S.R. 204/145 [33] Germany Prim E xammer---Damel E.Wyman D 51 750 Asrislan! Examiner-P. E. Konopka Attorney-Burgess,Dinklage & Sprung [54] PROCESS FOR THE REMOVAL OF METAL POWDER AND LOWMETAL OXIDES FROM THE SURFACES 0F BUNDLES 0F WIRE WHICH HAVE ABSTRACT:Improvement in the known process for remov- BEEN ETCIIED WITH SODIUMHYDRIDE t l f t l ts u b 7 Claims 1 Drawing g mg rus or sea e rom me a oec especra y wires, y 1mmerslon of the ob ect 1n caustic soda, causticpotash, or a mix- [52] US. Cl 204/141, ture thereof, followed byinducing an electric current to pass 204/145 R, 204/145 F therethroughwhile maintaining the object in an alkaline medi- [51] Int. Cl Cl0b 1/06um which improvement involves using lye of at least 60 per- [50] Fieldof Search 204/1451, cent concentration as the alkaline bath andoperating at up to I45, 141, 140 about 25C. over the solidificationpoint of the alkaline bath.

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ATTORNEYS.

PROCESS FOR THE REMOVAL OF METAL POWDER AND LOW METAL OXIDES FROM THESURFACES OF BUNDLES OF WIRE WHICH HAVE BEEN ETCHED WITH SODIUM HYDRIDEThis invention is directed to the cleaning of metals. It is morespecifically related to the removal of rust and/or scale from wirecoils.

Processes are known for reducing rust or scale on metal surfaces byimmersing the metal objects in a bath consisting of molten caustic sodaand/or caustic potash plus sodium hydride in a quantity of 0.5 to 3percent of the weight of the caustic soda and/or caustic potash, andthen removing the reduced coating from the metal surface by electricaltreatment in an alkaline medium. The electrical treatment involvespassing a current through the object, first using the object as ananode, and then by polarity reversal, using the object as a cathode. lnthe case of bundles of wire, particularly a coil, it is difiicult toremove the rust or scale from the interior of the bundle. Completeremoval of the rust or scale is achieved only on the outer surface ofthe bundle. This is probably due to the fact that the current lines runonly in the outer surface of the bundle.

It is an object of this invention to provide an improved process forremoval of rust and/or scale from a metal object, particularly a wirecoil.

Other and additional objects of this invention will become apparent froma consideration of this entire specification including the claims andthe drawing hereof.

ln accord with and fulfilling these objects, one aspect of thisinvention resides in a process for the removal of rust and/or scale fromthe surface of a bundle of wire which process comprises etching thebundle of wire in molten caustic soda or molten caustic potashcontaining sodium hydride; and then passing an electric current throughthe bundle of wire while such wire is immersed in an alkaline mediumhaving a lye content of at least about 60 percent. The alkaline bath ismaintained at up to about 25 C., preferably about to 20 C., above itssolidification point. During the electrical treatment the polarity ofthe current is reversed so that for part of the treatment the wirebundle is the anode and for part it is the cathode.

Surprisingly it has been found that the rust or scale can be completelyremoved, even in the interior of the wire bundle, if the temperature andconcentration conditions of the invention are sustained in the lye bath.The metal compounds developing from the metal powder and the low metaloxides in the post-treatment settle out and are captured at the bottomof the lye bath in separate containers. This process may be carried outwith agitation or in a quiescent state. ln steady operation the bath hasan average iron content of approximately 0.1% Fe O ln the anodic andcathodic process the current passes through the suspended wire bundle,the lye bath and, as the counterelectrode, a plate made ofcorrosion-resistant steel s1 spended in the lye bath. The anodictreatment is completed as soon as a yellowish violet coating has formedin the interior of the bundle.

The process of this invention can be improved if an additional cathodeis inserted through the center of the suspended wire bundle. ln thecathodic treatment that follows, and which is accomplished merely byreversing polarity while the arrangement remains the same, the yellowishviolet coating is dissolved and is also chipped ofi by the cathodicevolution of hydrogen, so that the wire surface becomes metallicallyclean. Since the course of the current lines is disturbed at the pointwhere the wire bundle contacts its hanger, and for this reason theanodic and cathodic etching does not take place to the desired extent atthis point, it is desirable to change the position of the bundle on thehanger after half of the anodic etching time and half of the cathodicetching time have passed, so that the previous points of contact orhearing points become freely accessible to the flow of current.

This invention will be better understood by reference to theaccompanying drawing, the single figure of which is a schematic sideelevation of the arrangement of parts in the lye bath during anodic andcathodic treatment.

The following examples are illustrative of this invention without beinglimiting on the scope thereof.

Example 1 A -kilogram wire bundle having an inside diameter of 400 to500 mm., a wire diameter of 3 mm., and a scale content of 0.3 percent,is immersed, after hydride etching, into a lye bath containing 60%NaOH/KOH. The bath temperature is 70 C. The bundle is treated anodicallyfor 20 minutes at a current of 1,500 amperes. A violet coating forms inthe core of the bundle. In the cathodic treatment then following, whichis also performed for 20 minutes at 1,500 amperes, the coating thatdeveloped in the anodic treatment comes of? completely.

At the middle of the anodic treatment and at the middle of the cathodictreatment, the point of contact between the wire bundle and its hangeris changed by turning the wire bundle. Finally the wire is rinsed incold water and protected against further corrosion by immersion in alime bath.

The same procedure is followed in all the further examples set forthbelow.

Example 2 A wire bundle of the same kind as in example I is treatedanodically and cathodically at 65 C. in a 60 percent caustic soda lyeafter the hydride etching. With a current of 1,500 amperes, the blackcoating on the metal is transformed within 20 minutes into a yellowishviolet compound extending all the way into the core of the bundle. Acathodic treatment at 1,500 amperes for 20 minutes is required forcomplete cleaning. Then the bundle is rinsed in cold water and dipped inmilk of lime.

Example 3 A wire bundle as in examples 1 and 2 is immersed, afterhydride etching, into 60% KOH at a temperature of 75C.

In the anodic post-treatment at 1,500 amperes, a yellowish violetcoating forms within 20 minutes, which is completely removed within 20minutes by reversing the polarity.

The wire bundle is then rinsed with water and protected against furtherrusting with lime.

Example 4 A wire bundle of the same kind as in examples l to 3 isimmersed after hydride etching into a bath of molten 100% NaOh/KOH at215 C.

The anodic treatment is performed at 1,500 amperes for 5 minutes. Theyellowish violet coating that forms is not resistant and largelyredissolves. What is left is an extremely thin yellowish coating whichis entirely removed by the reversal of polarity (5 min. at 1,500 amp.).

The bundle is washed in cold water and then dipped in milk of lime.

Example 5 A wire bundle as in examples 1 to 4 is immersed in a bath ofmolten 100% NaOH at a temperature of 330 C.

After 5 minutes of anodic treatment at 1,500 amperes, the bundle turnsgolden yellow all the way into the core.

The bundle is then washed in cold water and dipped in milk of lime.

Example 6 A bundle of wire as in examples l to 5 is immersed into a bathof 100 percent molten KOH at 370 C. After 5 minutes of anodicpost-treatment at 1,500 amperes the bundle has assumed a yellowish colorextending all the way into the core. For cathodic cleaning, 5 minutesare required. The bundle is washed in cold water to remove all thealkali and is then dipped in milk of lime.

The electric current intensities stated in all examples can be reduceddown to about 1,000 amperes, although longer cleaning periods will thenbe necessary.

What is claimed is:

l. in the process for removing scale and rust from metal thereof. wirebundles by etching such in molten caustic "comprising 3. The improvedprocess claimed in claim 1 wherein said sodium hydride and at least onemember selected from the bath isabout 60% KOH/NaOi-l and isat about 70C.group consisting of caustic soda and caustic potash and then 4. Theimproved process claimed in claim 1 wherein said subjecting such toelectric treatment with a current of at least 5 bath 9" 50% and 15abofll I about 1,000 amperes" has been inserted in a liquid alkaline TImproved P l 1 when!" Bald bath both as an anode and as a cathode; theimprovement bath"; abQut 60% and is 75 which comprises providing saidalkaline bath as at least about T lmpmved Process clfnmed 1 wherein 60percent lye and at a temperature up to about 25 C. above 533115 9 /K Hand mat about 2 l5 C. l the solidification poimthereofi l0 7. Theimproved process claimed in claim 1 wherein said 2. The improved processclaimed in claim 1 wherein said bath 100% a! abou 330 liquid bath isabout l0 to C. above the solidification point

2. The improved process claimed in claim 1 wherein said liquid bath isabout 10 to 20* C. above the solidification point thereof.
 3. Theimproved process claimed in claim 1 wherein said bath is about 60%KOH/NaOH and is at about 70* C.
 4. The improved process claimed in claim1 wherein said bath is about 60% NaOH and is at about 65* C.
 5. Theimproved process claimed in claim 1 wherein said bath is about 60% KOHand is at about 75* C.
 6. The improved process claimed in claim 1wherein said bath is 100% NaOH/KOH and is at about 215* C.
 7. Theimproved process claimed in claim 1 wherein said bath is 100% NaOH andis at about 330* C.